Ceramic heater for a gas measuring sensor

ABSTRACT

Proposed is a heater arrangement for a measuring sensor for determining components in gases, particularly in exhaust gases of internal combustion engines. The heater arrangement comprises at least two heating elements (10, 11) which are disposed at least partly one above the other and electrically insulated from one another by means of at least one insulating layer. A contacting member (14) laid through the insulating layer from one heating element (10) to the other heating element (11) is provided in such a manner that the heating elements (10, 11) are switched in series one behind the other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is based on a heater arrangement for a measuring sensorfor determining components in gases, particularly in exhaust gases ofinternal combustion engines, according to the generic type of the mainclaim.

2. Description of the Related Art

From DE-OS 2,913,866 it is known, in a planar measuring sensor, todispose two heating elements electrically insulated from the measuringelement and among themselves by an insulating layer in two planes, oneabove the other. Each of the two heating elements uses a heat-conductingtrack and two heater connection tracks, which are positioned withrespect to the side of the measuring sensor facing away from themeasured gas such that they can respectively be connected to a currentsource there.

SUMMARY OF THE INVENTION

In contrast, the heater arrangement having the characterizing featuresof the main claim has the advantage that the heating capacity isincreased, so that the measuring sensor possesses a shorter readyingtime for regulation. Particularly when used as rod heaters in lambdasensors, an improvement in the sensitivity with respect to impurities isadditionally achieved.

Advantageous modifications and improvements of the heater arrangementdisclosed in the main claim are possible with the measures outlined inthe dependent claims. A particularly high heating capacity can beattained when the heat-conductor tracks of the individual heatingelements are configured to have at least partially a meandering shape. Aparticularly homogenous temperature distribution is achieved when, witha heat-conducting track segment guided inside and one guided outside,the inside heat-conducting track segment is configured to be wider thanthe outside heat-conducting track. To avoid thermal overload, it isadvisable to make the spacings of two adjacent heat-conducting tracks inone plane as large as possible, and the heat-conducting tracks have aminimum spacing from the edge of the ceramic substrate.

BRIEF DESCRIPTION OF THE DRAWING

A plurality of embodiments of the invention are represented in thedrawing and described in detail in the following description.

FIG. 1 shows an exploded representation of two heating elements, eachhaving a heat-conducting track that has an inside and an outsidesegment,

FIG. 2 shows an exploded representation of two heating elements, eachhaving a heat-conducting track extending at the edge of a ceramicsubstrate,

FIG. 3 shows an exploded representation of two heater elements, eachhaving a heat-conducting track extending to the inside from the outside,

FIG. 4 shows a special embodiment of the heater arrangement according toFIG. 2, in which respectively an outside heat-conducting track has ameandering-shaped course,

FIG. 5 shows an exploded representation of a heating element disposedbetween two heater connection tracks, and FIG. 6 shows an explodedrepresentation of four heating elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments represented in the drawing each show heating elementshaving the course of a heat-conducting track, heater connection tracksand heater terminals; but not the ceramic insulating layers disposedbetween the heating elements. In conjunction with the explodedrepresentations, however, it is easily conceivable that a ceramicinsulating layer be disposed, on the one hand, between the heatingelements and, on the other hand, the heating elements and heaterterminals.

The embodiment according to FIG. 1 shows a first heating element 10 anda second heating element 11. An insulating layer 1 is disposed betweenthe two heating elements 10 and 11. The insulating layer 1 is composedof, for example, one or a plurality of ceramic wafers of Al₂ O₃, ontowhose two large surfaces the heating elements 10 and 11 are printed, forexample by means of a tungsten printing paste.

The two heating elements 10 and 11 each have a heat-conducting track 20,21 and a heater connection track 30, 31. The heat-conducting track 20,21 extends on the two large surfaces of respective ceramic substrates 1,2 in such a manner that respectively two parallel-extendingheat-conducting track segments are at the edge of the ceramic wafers 1,2, between which an inwardly-guided, heat-conducting track segmenthaving a meandering shape lies.

The two heating elements 10 and 11 are preferably aligned with oneanother, so that the end of the heat-conducting track 20 of the firstheating element 10 comes to rest above the end of the heat-conductingtrack 21 of the second heating element 11. At this location a hole 4 isprovided in the insulating layer, through which one contacting member14, a so-called via, is laid (as shown in FIG. 2). An electricalconnection between the first heating element 10 and the second heatingelement 11 is thus produced. The contacting member 14 can be producedby, for example, dripping a tungsten paste into the hole provided in theinsulating layer. Heat-conducting tracks 20, 21 may have segments havingdifferent widths. The width of interior track segments 20", 21" ispreferably greater than that of exterior track segments 20', 21'.

In the present embodiment, a further ceramic insulating layer 3 forexample of Al₂ O₃, is respectively disposed on the first heating element10 and the second heating element 11. Located on the insulating layer 3covering the first heating element 10 is a first heater terminal 40, andon the insulating layer 2 covering the second heating element 11 is asecond heater terminal 41. A further hole, in which respectively afurther contacting member 18 for electrically connecting the heatingarrangement 40, 41 to the heater connection tracks 30, 31 is disposed(see FIG. 2), is provided in each of the two insulating layers 3, 2. Thetwo heater terminals 40, 41 are likewise printed onto the two insulatinglayers 3, 2 by means of a tungsten paste. The two heater terminals 40,41 are thus bare and can be used for contact with electricalconnections.

The embodiment according to FIG. 2 has essentially the same design asthe embodiment in FIG. 1, but the heat-conducting tracks 20 and 21 ofthe two heating elements 10 and 11 are guided differently. In thisembodiment the heat-conducting tracks 20 and 21 respectively have largerspacing than in the embodiment in FIG. 1. The heat-conducting tracks 20and 21 are respectively guided along the edge of the insulating layers1, 2 (not shown).

FIG. 3 shows a further embodiment of the heat-conducting tracks, inwhich the first and the second heat-conducting track 20, 21 are bothguided along the edge of the insulating layer, and respectively back inthe direction of the front edge of the insulating layer with aheat-conducting track segment, so that the two ends of theheat-conducting tracks 20 and 21 come to lie one above the other in thecenter of the front region of the insulating layer. In this embodimentthe spacing of the heat-conducting track 20, 21 is respectively betweenthat of the embodiments in FIGS. 1 and 2.

A further embodiment of the heat-conducting tracks according to theembodiment shown in FIG. 2 is based on FIG. 4. In this instance theheat-conducting tracks 20 and 21 likewise extend at the edge of theinsulating layer, and respectively one of the longitudinal segments ofthe heat-conducting track has a meandering course 24, 25. Thelongitudinal segment having the meandering course 24, 25 is configuredsuch that the meandering course 24 of the first heating element 10 islocated opposite the straight segment of the heat-conducting track 21 ofthe second heating element 11, and the meandering segment 25 of thesecond heating element 11 is located opposite the straight segment ofthe heat-conducting track 20 of the first heating element 10. Because ofthis embodiment, a more intense temperature field is created toward thenarrow sides of the heater arrangement than in the previously-describedembodiments. In the embodiments shown in FIGS. 1 through 4, the ends ofthe first heat-conducting track 20 and the second heat-conducting track21 are located respectively aligned one above the other, so that thecontacting member 14 is effected as already described in the firstembodiment according to FIG. 1.

A further embodiment is shown in FIG. 5. In this instance the firstheating element 10 and the second heating element 11 have only oneheater connection track 30, 31. The first heater connection track 30 isdisposed on a first insulating layer, not shown. The second heaterconnection track 31 is located on a second insulating layer, likewisenot shown. A third heating element 12 is located between the twoinsulating layers. The third heating element 12 is formed from only oneheat-conducting track 22 that extends at the edge of the two insulatinglayers, so that the heat-conducting track 22 ends above the end of thefirst heater connection track 30 and above the end of the second heaterconnection track 31. The ends of heat-conducting track 22 and heaterconnection tracks 30, 31, which are disposed one above the other, arerespectively connected to one another by means of a first and a secondcontacting member 15, 16. The contacting members 15, 16 are effected inthe same way as described in the embodiment according to FIG. 1. Thesame applies for the arrangement and production of the heater terminals40, 41 and the terminal contacting members 18.

Finally, an embodiment follows from FIG. 6 in which four heatingelements 10, 11, 12 and 13 are provided. Each of the heating elements10, 11, 12 and 13 lies in respectively one plane and is separated fromthe adjacent heating element by means of an insulating layer, not shown.The first and second heating elements 10, 11 respectively have, asalready described in the previous embodiments, one heat-conducting track20, 21 and one heater connection track 30, 31. The heat-conductingtracks 20, 21 extend symmetrically with respect to a plane of symmetryperpendicular to the plane of the layer. The heat-conducting tracks 20,21 each have a segment that extends along the longitudinal side of theinsulating layer and a segment that extends at a right angle theretoalong the narrow side of the insulating layer. The third heating element12 disposed beneath the first heating element 10 extends from theprojection of the end of the first heat-conducting track 20 along thelongitudinal side of the insulating layer, and bends at a right angle,in the direction of the longitudinal side located opposite, to beneaththe first heat-conducting track 20. The fourth heat-conducting track 23extends along the longitudinal side of the insulating layer, and beginsat the location of the projection of the second end of the thirdheat-conducting track 22, and ends at the location of the projection ofthe end of the second heat-conducting track 21. Hence, the ends of theheat-conducting tracks 20, 21, 22, 23 lie one above the other in such away that an electrical connection is possible by means of the first,second and third contacting members 15, 16, 17 extending through theinsulating layers. The embodiment of the contacting members 15, 16, 17,and the embodiment of the heater terminals 40, 41, as well as theassociated terminal contacting members 18, are effected as alreadydescribed in the first embodiment.

It is also conceivable, in addition to the insulating layers, to disposethe heater arrangement on further ceramic substrate layers. Likewise,the insulating layers disposed on the first and second heating elements10, 11 can be replaced by thermally well-conductive ceramic layers.Furthermore, it is conceivable to lay the electrical terminals directlyonto the heater connection tracks 30, 31.

The application of the invention is not limited to the described rodheaters for lambda finger sensors. It is also conceivable to configurethe heater arrangement for planar sensors, in which case one of theouter-lying heating elements is connected to a measuring element in anelectrically-insulated manner. Such measuring elements can be, forexample, potentiometric or polarographic sensor elements or resistancemeasuring sensors.

What is claimed is:
 1. A ceramic heater for a measuring sensor fordetermining components in gases including exhaust gases of internalcombustion engines, comprising:first and second ceramic substrates whichare stacked with respect to one another, at least one additional ceramicsubstrate provided between the first and second ceramic substrates, anda third ceramic substrate which is positioned on top of the firstceramic substrate and functions as a cover layer, the first, the second,the third, and the at least one additional ceramic substrate havingdefined therein respective first, second, third, and at least oneadditional through-holes; a first heater element consisting essentiallyof a heater connection track which is provided on a surface of the firstceramic substrate; a second heater element consisting essentially of aheater connection track which is provided on a surface of the secondceramic substrate; at least one additional heater element consisting ofa heat-conducting track which is provided on a respective surface of oneof the at least one additional ceramic substrate; a first heaterterminal provided on a surface of the third ceramic substrate which isoriented outwardly of the ceramic heater and a second heater terminalprovided on a surface of the second ceramic substrate which is orientedoutwardly of the ceramic heater; a contacting member positioned withinthe first through-hole and in contact with the heater connection trackof the first heater element and the heat-conducting track of the atleast one additional heater element; at least one additional contactingmember each positioned within a respective at least one additionalthrough-hole in the at least one additional ceramic substrate and incontact with the heat-conducting track of the at least one additionalheater element and the heater connection track of the second heatingelement whereby the respective heater elements are electricallyconnected in series with one another; and further contacting memberspositioned respectively within the second and third through-holes and incontact with respective heater connection tracks of the first and secondheater elements, whereby the first and second heater elements areelectrically connected to respective heater terminals.
 2. The ceramicheater according to claim 1,wherein a plurality of the at least oneadditional ceramic substrate is provided, each additional ceramicsubstrate having a heater element consisting essentially of aheat-conducting track provided on a surface thereof and havingrespective through-holes defined therein, and the heater elements beingdisposed at least partly one above the other with a respective ceramicsubstrate positioned therebetween to provide electrical insulation, andwherein further contacting members are positioned within respective onesof the respective through-holes and in contact with respectiveheat-conducting tracks whereby the heat-conducting tracks areelectrically connected in series with one another.
 3. The ceramic heateraccording to claim 2, wherein the respective heat-conducting tracks havea path having at least one shape selected from the group consisting of ameandering shape and a zig-zag shape.
 4. The ceramic heater according toclaim 1, wherein the respective heat-conducting tracks each have atleast one interior and at least one exterior heat-conducting tracksegment provided respectively in interior and exterior regions of thesurfaces of respective ceramic substrates and having respective widths,andwherein the width of respective at least one interior heat-conductingtrack segments is greater than the width of respective at least oneexterior heat-conducting track segments.
 5. The ceramic heater accordingto claim 1, wherein the first, second, and at least one additionalheater elements are resistance heaters which have a layer form.
 6. Aceramic heater for a measuring sensor for determining components ingases including exhaust gases of internal combustion engines,comprising:first and second ceramic substrates which are stacked withrespect to one another, at least one additional ceramic substrateprovided between the first and second ceramic substrates, and a thirdceramic substrate which is positioned on top of the first ceramicsubstrate and functions as a cover layer, the first, the second, thethird, and the at least one additional ceramic substrate having definedtherein respective first, second, third, and additional through-holes; afirst heater element which is provided on a surface of the first ceramicsubstrate and which has a heat-conducting track and a heater connectiontrack in contact with one another; a second heater element which isprovided on a surface of the second ceramic substrate and which has aheat-conducting track and a heater connection track in contact with oneanother; at least one additional heater element consisting of aheat-conducting track provided on a respective surface of one of the atleast one additional ceramic substrate; a first heater terminal providedon a surface of the third ceramic substrate which is oriented outwardlyof the ceramic heater and a second heater terminal provided on a surfaceof the second ceramic substrate which is oriented outwardly of theceramic heater; a contacting member positioned within the firstthrough-hole and in contact with the heat-conducting track of the firstheater element and the heat-conducting track of the at least oneadditional heater element; at least one additional contacting memberpositioned within a respective at least one additional through-hole inthe at least one additional ceramic substrate and in contact with theconducting tracks of adjacent heater elements; and further contactingmembers positioned respectively within the second and thirdthrough-holes and in contact with respective heater connection tracks ofthe first and second heater elements whereby the first and secondheater-elements are electrically connected to respective heaterterminals.
 7. The ceramic heater according to claim 6, where in twoadditional heater element, are provided, wherein the respectiveheat-conducting tracks of the first, the second and the two additionalheater elements have respective ends, andwherein two additionalcontacting members are provided, each of the two additional contactingmembers connecting the end of one heat-conducting track of one heatingelement to the end of another heat-conducting track of another heatingelement.
 8. The ceramic heater according to claim 6, wherein therespective heat-conducting tracks have a path having at least one shapeselected from the group consisting of a meandering shape and a zig-zagshape.
 9. The ceramic heater according to claim 6, wherein therespective heat-conducting tracks each have at least one interior and atleast one exterior heat-conducting track segment provided respectivelyin interior and exterior regions of the surfaces of the respectiveceramic substrates and having respective widths, andwherein the width ofrespective at least one interior heat-conducting track segments isgreater than the width of respective at least one exteriorheat-conducting track segments.
 10. The ceramic heater according toclaim 6, wherein the first, the second, and the at least one additionalc heating elements are resistance heaters which have a layer form.